config: disable thread safety analysis on COFF
config: disable thread safety analysis on COFF

clang cannot properly handle __declspec and __attribute__ on classes
right now.  This prevents the shared_mutex tests from working.  Disable
the use of the annotation on COFF targets.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@294958 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx